Two-component coating compositions containing silane adhesion promoters

ABSTRACT

The present invention relates to two-component coating compositions containing  
     a) a polyisocyanate component,  
     b) an isocyanate-reactive component that contains less than 3% by weight, based on the weight of component b), of an aromatic polyamine and  
     c) 0.1 to 1.8 wt. %, based on the weight of components a) and b), of a compound containing at least one epoxy group and at least one alkoxysilane group.  
     The present invention also relates to substrates coated with these coating compositions, in particular metal substrates.

[0001] This is a Continuation-In-Part application of U.S. Ser. No.09/747,057, filed Dec. 22, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to two-component coatingcompositions containing silane adhesion promoters having epoxy groupsand alkoxysilane groups and to their use for preparing coatings havingimproved adhesion, especially wet adhesion.

[0004] 2. Description of the Prior Art

[0005] Two-component coating compositions containing a polyisocyanatecomponent and an isocyanate-reactive component, preferably apolyhydroxyl compound, are known and can be used to coat a variety ofsubstrates. One of the deficiencies of these coatings is that they donot possess adequate wet adhesion, which is a critical requirement forcoatings used underground, e.g., as coatings for oil and gastransmission pipelines.

[0006] Coatings previously used for this application have suffered fromother problems. Asphaltic coatings are biodegradable and not suitablefor long term (20 to 50 years) use. Coal tar coatings are not usedbecause of toxicity. Liquid epoxy coatings require applicationtemperatures of >55° C. and cure too slowly for production use in thefield. Polyolefin coatings do not maintain adhesion under cathodicprotection.

[0007] High performance coatings are needed. Known polyurethane coatingshave the ability to be rapidly cured, but do not have the wet adhesionnecessary for this application.

[0008] Accordingly, it is an object of the present invention to providecoating compositions that are suitable for preparing coatings havingimproved adhesion, especially wet adhesion.

[0009] This object may be achieved with the two-component coatingcompositions according to the present invention which contain compoundscontaining epoxy and alkoxysilane groups as adhesion promoters.

[0010] The use of silanes as adhesion promoters has been suggested. Aproduct information bulletin from OSi Specialties discloses the use ofseveral silane compounds as adhesion promotors for various coatingresins, including polyurethanes. However, as shown by the comparisonexamples of the present application, most of the disclosed silanecompounds were not very effective for improving the adhesion, especiallythe wet adhesion, of two-component polyurethane coating compositions.Accordingly, it is apparent that the reference to polyurethanes was areference to one-component, fully reacted polyurethanes.

SUMMARY OF THE INVENTION

[0011] The present invention relates to two-component coatingcompositions containing

[0012] a) a polyisocyanate component,

[0013] b) an isocyanate-reactive component that contains less than 3% byweight, based on the weight of component b), of an aromatic polyamineand

[0014] c) 0.1 to 1.8 wt. %, based on the weight of components a) and b),of a compound containing at least one epoxy group and at least onealkoxysilane group.

[0015] The present invention also relates to substrates coated withthese coating compositions, in particular metal substrates.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred compounds containing epoxy groups and alkoxysilanegroups that are used as component c) in the compositions according tothe present invention correspond to the following formula

[0017] wherein

[0018] x represents identical or different organic groups which areinert to isocyanate groups below 100° C., provided that at least one ofthese groups is an alkoxy group, preferably alkyl or alkoxy groupshaving 1 to 4 carbon atoms and more preferably alkoxy groups, and

[0019] Y represents a linear or branched alkylene group containing 1 to8 carbon atoms, preferably a linear group containing 2 to 4 carbon atomsor a branched group containing 5 to 6 carbon atoms, more preferably alinear group containing 3 carbon atoms.

[0020] Especially preferred are compounds in which X represents methoxy,ethoxy groups or propoxy groups, more preferably methoxy or ethoxygroups and most preferably methoxy groups, and Y is a propylene group.

[0021] Examples of suitable compounds containing epoxy groups andalkoxysilane groups include 2-glycidoxyethyl-dimethylmethoxysilane;6-glycidoxyhexyl-tributoxysilane; 3-glycidoxypropyl-trimethoxysilane;3-glycidoxypropyl-triethoxysilane;3-glycidoxypropyl-methyidiethoxysilane;5-glycidoxypentyl-trimethoxysilane; 5-glycidoxypentyl-triethoxysilaneand 3-glycidoxypropyl-triisopropoxysilane. Especially preferred is3-glycidoxypropyl-trimethoxysilane, which is available from OSiSpecialties as Silquest A-187.

[0022] Suitable polyisocyanates for use as component a) in thecompositions of the present invention are selected from monomericpolyisocyanates, polyisocyanate adducts and NCO prepolymers, preferablypolyisocyanate adducts and NCO prepolymers and more preferably NCOprepolymers. The polyisocyanates have an average functionality of 1.8 to6, preferably 2 to 6 and more preferably 2 to 4.

[0023] Suitable monomeric diisocyanates are represented by the formula

R(NCO)₂

[0024] in which R represents an organic group obtained by removing theisocyanate groups from an organic diisocyanate having a molecular weightof about 112 to 1,000, preferably about 140 to 400. Diisocyanatespreferred for the process according to the invention are those in whichR represents a divalent aliphatic hydrocarbon group having 4 to 40,preferably 4 to 18 carbon atoms, a divalent cycloaliphatic hydrocarbongroup having 5 to 15 carbon atoms, a divalent araliphatic hydrocarbongroup having 7 to 15 carbon atoms or a divalent aromatic hydrocarbongroup having 6 to 15 carbon atoms.

[0025] Examples of the suitable organic diisocyanates include1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate,2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12-dodecamethylenediisocyanate, cyclohexane-1,3- and -1,4-diisocyanate,1-isocyanato-2-isocyanatomethyl cyclopentane,1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophoronediisocyanate or IPDI), bis-(4-isocyanatocyclohexyl)-methane,2,4′-dicyclohexyl-methane diisocyanate, 1,3- and1,4-bis-(isocyanatomethyl)-cyclohexane,bis-(4-isocyanato-3-methyl-cyclohexyl)-methane,α,α,α′,α′-tetramethyl-1,3- and/or -1,4-xylylene diisocyanate,1-isocyanato-1-methyl-4(3)-isocyanatomethyl cyclohexane, 2,4- and/or2,6-hexahydrotoluylene diisocyanate, 1,3- and/or 1,4-phenylenediisocyanate, 2,4- and/or 2,6-toluylene diisocyanate, 2,4-and/or4,4′-diphenyl-methane diisocyanate, 1,5-diisocyanato naphthalene andmixtures thereof.

[0026] Polyisocyanates containing 3 or more isocyanate groups such as4-isocyanantomethyl-1,8-octamethylene diisocyanate and aromaticpolyisocyanates such as 4,4′,4″-triphenylmethane triisocyanate andpolyphenyl polymethylene polyisocyanates obtained by phosgenatinganiline/formaldehyde condensates may also be used.

[0027] Preferred organic diisocyanates include 1,6-hexamethylenediisocyanate,1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophoronediisocyanate or IPDI), bis-(4-isocyanato-cyclohexyl)-methane,1-isocyanato-1-methyl-4(3)-isocyanatomethyl cyclohexane, 2,4- and/or2,6-toluylene diisocyanate, and 2,4- and/or 4,4′-diphenylmethanediisocyanate.

[0028] Suitable polyisocyanate adducts for use as component a) are thoseprepared from the preceding monomeric polyisocyanates and containingisocyanurate, uretdione, biuret, urethane, allophanate, iminooxadiazinedione, carbodiimide and/or oxadiazinetrione groups. The polyisocyanatesadducts, which preferably have an NCO content of 5 to 30% by weight,include:

[0029] 1) Isocyanurate group-containing polyisocyanates which may beprepared as set forth in DE-PS 2,616,416, EP-OS 3,765, EP-OS 10,589,EP-OS 47,452, U.S. Pat. Nos. 4,288,586 and 4,324,879. Theisocyanato-isocyanurates generally have an average NCO functionality of3 to 3.5 and an NCO content of 5 to 30%, preferably 10 to 25% and mostpreferably 15 to 25% by weight.

[0030] 2) Uretdione diisocyanates which may be prepared by oligomerizinga portion of the isocyanate groups of a diisocyanate in the presence ofa suitable catalyst, e.g, a trialkyl phosphine catalyst, and which maybe used in admixture with other aliphatic and/or cycloaliphaticpolyisocyanates, particularly the isocyanurate group-containingpolyisocyanates set forth under (1) above.

[0031] 3) Biuret group-containing polyisocyanates which may be preparedaccording to the processes disclosed in U.S. Pat. Nos. 3,124,605;3,358,010; 3,644,490; 3,862,973; 3,906,126; 3,903,127; 4,051,165;4,147,714; or 4,220,749 by using co-reactants such as water, tertiaryalcohols, primary and secondary monoamines, and primary and/or secondarydiamines. These polyisocyanates preferably have an NCO content of 18 to22% by weight and an average NCO functionality of 3 to 3.5.

[0032] 4) Urethane group-containing polyisocyanates which may beprepared in accordance with the process disclosed in U.S. Pat. No.3,183,112 by reacting excess quantities of polyisocyanates, preferablydiisocyanates, with low molecular weight glycols and polyols havingmolecular weights of less than 400, such as trimethylol propane,glycerine, 1,2-dihydroxy propane and mixtures thereof. The urethanegroup-containing polyisocyanates have a most preferred NCO content of 12to 20% by weight and an (average) NCO functionality of 2.5 to 3.

[0033] 5) Allophanate group-containing polyisocyanates which may beprepared according to the processes disclosed in U.S. Pat. Nos.3,769,318, 4,160,080 and 4,177,342. The allophanate group-containingpolyisocyanates have a most preferred NCO content of 12 to 21% by weightand an (average) NCO functionality of 2 to 4.5.

[0034] 6) Isocyanurate and allophanate group-containing polyisocyanateswhich may be prepared in accordance with the processes set forth in U.S.Pat. Nos. 5,124,427, 5,208,334 and 5,235,018, the disclosures of whichare herein incorporated by reference, preferably polyisocyanatescontaining these groups in a ratio of monoisocyanurate groups tomono-allophanate groups of about 10:1 to 1:10, preferably about 5:1 to1:7.

[0035] 7) Iminooxadiazine dione and optionally isocyanurategroup-containing polyisocyanates which may be prepared in the presenceof special fluorine-containing catalysts as described in DE-A 19611849.These polyisocyanates generally have an average NCO functionality of 3to 3.5 and an NCO content of 5 to 30%, preferably 10 to 25% and mostpreferably 15 to 25% by weight.

[0036] 8) Carbodiimide group-containing polyisocyanates which may beprepared by oligomerizing di- or polyisocyanates in the presence ofknown carbodiimidization catalysts as described in DE-PS 1,092,007, U.S.Pat. No. 3,152,162 and DE-OS 2,504,400, 2,537,685 and 2,552,350.

[0037] 9) Polyisocyanates containing oxadiazinetrione groups andcontaining the reaction product of two moles of a diisocyanate and onemole of carbon dioxide.

[0038] Preferred polyisocyanate adducts are the polyisocyanatescontaining isocyanurate, uretdione, biuret, iminooxadiazine dione and/orallophanate groups.

[0039] The NCO prepolymers, which may also be used as polyisocyanatecomponent a), are prepared from the previously described monomericpolyisocyanates or polyisocyanate adducts, preferably monomericdiisocyanates, and polyhydroxyl compounds containing at least twohydroxyl groups. These polyhydroxyl compounds include high molecularweight compounds having molecular weights of 500 to about 10,000,preferably 800 to about 8,000, and more preferably 1800 to 8,000, andoptionally low molecular weight compounds having molecular weights below500. The molecular weights are number average molecular weights (M_(n))and are determined by end group analysis (OH number). Products obtainedby reacting polyisocyanates exclusively with low molecular weightcompounds are polyisocyanates adducts containing urethane groups and arenot considered to be NCO prepolymers.

[0040] Examples of the high molecular weight compounds are polyesterpolyols, polyether polyols, polyhydroxy polycarbonates, polyhydroxypolyacetals, polyhydroxy polyacrylates, polyhydroxy polyester amides andpolyhydroxy polythioethers. The polyether polyols, polyester polyols andpolycarbonate polyols are preferred. Especially preferred are thepolyether polyols.

[0041] Examples of suitable high molecular weight polyhydroxyl compoundsinclude polyether polyols, which may be obtained in known manner by thealkoxylation of suitable starter molecules. Examples of suitable startermolecules include polyols, water, organic polyamines having at least twoN—H bonds and mixtures thereof. Suitable alkylene oxides for thealkoxylation reaction are preferably ethylene oxide and/or propyleneoxide, which may be used in sequence or in admixture.

[0042] Also suitable for preparing the prepolymers are polyester polyolsprepared from low molecular weight alcohols and polybasic carboxylicacids such as adipic acid, sebacic acid, phthalic acid, isophthalicacid, tetrahydrophthalic acid, hexahydrophthalic acid, maleic acid, theanhydrides of these acids and mixtures of these acids and/or acidanhydrides. Polylactones having hydroxyl groups, particularlypoly-,-caprolactone, are also suitable for producing the prepolymers.

[0043] Other suitable polyols include polycarbonates having hydroxylgroups, which may be produced by the reaction of diols with phosgene ordiaryl carbonates such as diphenyl carbonate.

[0044] Further details concerning the low molecular weight compounds andthe starting materials and methods for preparing the high molecularweight polyhydroxy compounds are disclosed in U.S. Pat. No. 4,701,480,herein incorporated by reference.

[0045] These NCO prepolymers preferably have an isocyanate content of0.3 to 35% by weight, more preferably 0.6 to 25% by weight and mostpreferably 1.2 to 20% by weight. The NCO prepolymers are produced byreacting the diisocyanates with the polyol component at a temperature of40 to 120EC, preferably 50 to 100EC, at an NCO/OH equivalent ratio of1.3:1 to 20:1, preferably 1.4:1 to 10:1. If chain extension via urethanegroups is desired during the preparation of the isocyanate prepolymers,an NCO/OH equivalent ratio of 1.3:1 to 2:1 is selected. If chainextension is not desired, an excess of diisocyanate is preferably used,corresponding to an NCO/OH equivalent ratio of 4:1 to 20:1, preferably5:1 to 10:1. The excess diisocyanate may optionally be removed by thinlayer distillation when the reaction is completed. In accordance withthe present invention NCO prepolymers also include NCO semi-prepolymerswhich contain unreacted starting polyisocyanates in addition to theurethane group-containing prepolymers.

[0046] Suitable isocyanate-reactive components for use as component b)in the compositions of the present invention are the high and lowmolecular weight, polyols previously disclosed for preparing the NCOprepolymers, provided that component b) contains less than 3% by weight,preferably less than 2% by weight, more preferably less than 1% byweight and most preferably less than 0.5% by weight, based on the weightof component b), of aromatic polyamines, in particular stericallyhindered aromatic polyamines. Also suitable are the known high molecularweight amine-functional compounds, which may be prepared by convertingthe terminal hydroxy groups of the polyols previously described to aminogroups, and the high molecular weight polyaldimines disclosed in U.S.Pat. No. 5,466,771, herein incorporated by reference. The high molecularweight polyols are preferred.

[0047] The two-component coating compositions of the present inventionmay be prepared by mixing the individual components. Components a) andb) are present in an amount of sufficient to provide an equivalent ratioof isocyanate groups is isocyanate-reactive, preferably hydroxyl groupsof 0.8:1 to 1.2:1, preferably 0.9:1 to 1.1:1 and more preferably 1:1 to1.1:1. Component c) is present in an amount of at least 0.1%, preferablyat least 0.3% and more preferably 0.5%, based on the weight ofcomponents a) and b). The upper limit for the amount of component c) is1.8%, preferably 1.5% and more preferably 1.3%, based on the weight ofcomponents a) and b).

[0048] The two-component compositions generally may be eithersolvent-free or contain up to 70%, preferably up to 60% organicsolvents, based on the weight of components a) and b). Suitable organicsolvents include those which are known from polyurethane chemistry.

[0049] The compositions may also contain known additives, such ascatalysts, leveling agents, wetting agents, flow control agents,antiskinning agents, antifoaming agents, fillers (such as silica,aluminum silicates and high-boiling waxes), viscosity regulators,plasticizers, pigments, dyes, UV absorbers and stabilizers againstthermal and oxidative degradation.

[0050] The two-component compositions may be applied to any desiredsubstrates, such as wood, plastics, leather, paper, textiles, glass,ceramics, plaster, masonry, metals and concrete. They may be applied bystandard methods, such as spray coating, spread coating, flood coating,casting, dip coating, roll coating. The coating compositions may beclear or pigmented.

[0051] The two-component compositions are especially suitable forcoating substrates, preferably metal substrates such as pipes, whichwill be exposed to a wet environment.

[0052] The two-component compositions may be cured at ambienttemperature or at elevated temperatures, preferably at ambienttemperatures.

[0053] The invention is further illustrated but is not intended to belimited by the following examples in which all parts and percentages areby weight unless otherwise specified.

EXAMPLES

[0054] Polyisocyanate 1

[0055] 556 g of a distilled diphenylmethanediisocyanate (MDI)composition containing 65% 2,4′-MDI and 35% 4,4′-MDI were stirred at 60°C. Then a mixture of 222 g of a polyether diol made by propoxylation ofpropylene glycol (OH number 112) and 222 g of a tetrafunctionalpolyether made by propoxylation of ethylene diamine (OH number 60) wasadded dropwise, so that a maximum temperature of 65° C. was maintained.When an NCO content of 16% was reached, the prepolymer was diluted with1000 g of a crude MDI containing 40.5% 2,4-MDI, 49,5% 4,4′-MDI and 10%polymeric MDI. The final semi-prepolymer had an NCO content of 24% and aviscosity of 220 mPa.s at 230C.

[0056] Polyether Polyol I

[0057] A polypropylene oxide polyol having a functionality of 3, an OHnumber of 370 and an equivalent weight of 152 and initiated withtrimethylolpropane.

[0058] Polyether Polyol 2

[0059] A polypropylene oxide polyol initiated with glycerine, tippedwith ethylene oxide (PO:EO equivalent ratio 83:17), having afunctionality of 3, an OH number of 35 and an equivalent weight of 1600and containing 20% of the equimolar reaction product toluenediisocyanate and hydrazine (overall OH number 28).

[0060] Two-Component Coating Compositions

[0061] Two-component coating compositions were prepared from thefollowing ingredients: Parts Component I Polyether polyol 1 120Polyether polyol 2 60 1,4-butane diol 130 3,5-diethyl-toluene diamine 5Talc 125 Lamilar silicate¹ 70 Titanium dioxide 30 1:1 Blend of molecularsieve/caster oil² 50 Dibutyltin dilaurate 0.4 Silicone flow aid 0.2Component II Polyisocyanate 1 490 Silane additive See Table Black paste5

[0062] Two-component coating compositions were prepared from thepreceding ingredients and the amounts and types of the silane additivesset forth in the following tables. The compositions were applied at20-30 mils on hot-rolled, sand-blasted steel panels. The panels werecured at room temperature for two weeks.

[0063] To determine dry and wet adhesion the coated panels were placedon end in a container or water such that about two thirds of the coatingwas submerged. After 30 days the panel was removed and immediatelytested. The test was conducted by scribing an “X” on both the dry andwet areas of the panel. A knife was used to pick at the corners of the“X.” A rating scale of 1 to 10 was used as follows:

[0064] 1—no adhesion, coating falls off of panel

[0065] 5—moderate adhesion, but coating can be peeled off of panel

[0066] 7—strong adhesion, but coating can be peeled off of panel

[0067] 8—coating tears as it is peeled off of panel

[0068] 10—coating can only be cut off of panel

[0069] A rating of 7 is acceptable, a rating of 8 is a good result and arating of 10 is an excellent result. A rating of 6 or less isunacceptable for use as a pipeline coating. TABLE Amount AdhesionAdhesion Promoter (wt. %) Dry Wet None (Comp.) 0 2 23-glycidoxypropyl-trimethoxysilane³ 1 10 10 According to the invention3-isocyanatopropyltriethoxysilane⁴ (Comp.) 1 7 7Tris-[3-(trimethoxysilyl)propyl]isocyanurate⁵ 1 8 8 (Comp.)3-mercaptopropyl-trimethoxysilane⁶ (Comp.) 1 3 33-aminopropyl-trimethoxysilane⁷ (Comp.) 1 3 6N-(2-aminoethyl)-3-aminopropyl- 1 2 2 trimethoxysilane⁸ (Comp.)Triaminofunctionalsilane⁹ (Comp.) 1 3 3 3-ureidopropyl-trialkoxysilane¹⁰(Comp.) 1 3 3 Bis-(3-trimethoxysilylpropyl)amine¹¹ (Comp.) 1 3 3Silquest Wet Link 78 additive (Comp.) 1 4 5

[0070] The examples demonstrate that it is possible using the adhesionpromoters according to the invention containing epoxy and alkoxysilanegroups to provide excellent adhesion, especially wet adhesion. Thisdegree of adhesion cannot be provided by other known silane adhesionpromoters when used in similar amounts.

[0071] Although the invention has been described in detail in theforegoing for the purpose of illustration, it is to be understood thatsuch detail is solely for that purpose and that variations can be madetherein by those skilled in the art without departing from the spiritand scope of the invention except as it may be limited by the claims.

What is claimed is:
 1. A two-component coating composition comprising a)a polyisocyanate component, b) an isocyanate-reactive component thatcontains less than 3% by weight, based on the weight of component b), ofan aromatic polyamine and c) 0.1 to 1.8 wt. %, based on the weight ofcomponents a) and b), of a compound containing at least one epoxy groupand at least one alkoxysilane group.
 2. The composition of claim 1wherein the compound containing epoxy groups and alkoxysilane groupsthat are used as component c) in the compositions according to thepresent invention correspond to the following formula

wherein X represents identical or different organic groups which areinert to isocyanate groups below 100° C., provided that at least one ofthese groups is an alkoxy group, and Y represents a linear or branchedalkylene group containing 1 to 8 carbon atoms.
 3. The composition ofclaim 2 wherein X represents identical or different alkyl or alkoxygroups, provided that at least one of these groups is an alkoxy group,and Y represents a linear or branched alkylene group containing 2 to 4carbon atoms.
 4. The composition of claim 2 x represents identical ordifferent alkoxy groups and Y represents a linear alkylene groupcontaining 3 carbon atoms.
 5. The composition of claim 1 whereincomponent c) is present in an amount of 0.5 to 1.5 wt. %, based on theweight of components a) and b).
 6. The composition of claim 2 whereincomponent c) is present in an amount of 0.5 to 1.5 wt. %, based on theweight of components a) and b).
 7. The composition of claim 3 whereincomponent c) is present in an amount of 0.5 to 1.5 wt. %, based on theweight of components a) and b).
 8. The composition of claim 4 whereincomponent c) is present in an amount of 0.5 to 1.5 wt. %, based on theweight of components a) and b).
 9. The composition of claim 1 whereinpolyisocyanate component a) comprises an NCO prepolymer prepared from apolyisocyanate and a polyether polyol, component b) comprises apolyhydroxyl compound and component c) is present in an amount of 0.5 to1.5 wt. %, based on the weight of components a) and b).
 10. Thecomposition of claim 2 wherein polyisocyanate component a) comprises anNCO prepolymer prepared from a polyisocyanate and a polyether polyol,component b) comprises a polyhydroxyl compound and component c) ispresent in an amount of 0.5 to 1.5 wt. %, based on the weight ofcomponents a) and b).
 11. The composition of claim 3 whereinpolyisocyanate component a) comprises an NCO prepolymer prepared from apolyisocyanate and a polyether polyol, component b) comprises apolyhydroxyl compound and component c) is present in an amount of 0.5 to1.5 wt. %, based on the weight of components a) and b).
 12. Thecomposition of claim 4 wherein polyisocyanate component a) comprises anNCO prepolymer prepared from a polyisocyanate and a polyether polyol,component b) comprises a polyhydroxyl compound and component c) ispresent in an amount of 0.5 to 1.5 wt. %, based on the weight ofcomponents a) and b).
 13. The composition of claim 9 wherein componentb) comprises a polyether polyol.
 14. The composition of claim 10 whereincomponent b) comprises a polyether polyol.
 15. The composition of claim11 wherein component b) comprises a polyether polyol.
 16. Thecomposition of claim 12 wherein component b) comprises a polyetherpolyol.
 17. A substrate coated with coating composition of claim
 1. 18.A metal substrate coated with the coating composition of claim 1.